This application is based on Japanese Patent Applications No. 2000-055472 filed Mar. 1, 2000, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention generally relates to a vibration damper installed in a vibrative member of a vehicle, for reducing vibration of the vibrative member. More particularly, the present invention is concerned with such a vibration damper which is novel in construction and which is suitably applicable to vibrative members such as suspension arms, sub frames, body panels, mounting brackets, and vibrative members used in an engine unit or an exhaustion system, so that the vibration damper exhibits an excellent damping effect with respect to vibrations excited in these vibrative members.
2. Description of the Related Art
As vibration damping means for damping or reducing vibration excited in vehicles such as an automotive vehicle, there are known (a) a mass damper wherein a mass member is fixed to a vibrative member, (b) a dynamic damper wherein a mass member is supported by and connected to the vibrative member via a spring member and (c) a damping material, which is a sheet-shaped elastic member and secured to the vibrative member. However, these conventional devices suffer from various potential problems. For example, (a) the mass damper and (b) the dynamic damper both require a relatively large mass of the mass member, and exhibit desired vibration damping effect only to significantly narrow frequency ranges. (c) The damping material suffers from difficulty in stably exhibiting a desired damping effect, since the damping effect of the damping material is likely to vary depending upon the ambient temperature.
The present assignee has been disclosed in International Publication WO 00/14429 a novel vibration damper used for an automotive vehicle, which includes a housing member having an inner space and fixed to the vibrative member, and an independent mass member which is accommodated in a inner space of the housing member without being bonded to the housing member, so that the independent mass member is displaceable or movable relative to the housing member, while being independent of the housing member. In the disclosed vibration damper, the independent mass member is moved into and impact the housing member, upon application of a vibrational load to the damper, whereby the vibration of the vibrative body is effectively reduced or absorbed based on loss or dissipation of energy caused by sliding friction generated between the abutting surfaces of the mass member and the housing member and caused by collision or impact of the independent mass member against the housing member. This proposed vibration damper is capable of exhibiting a high damping effect over a sufficiently wide frequency range of frequency of input vibrations, while having a relatively small mass of the mass member.
In order to stably establish a desired damping effect of the vibration damper disclosed in the above-indicated document, it is required to precisely control a distance of spacing or gap between the abutting surface of the independent mass member and the abutting surface of the housing member, as well as to obtain a sufficient mass of the independent mass member.
In the stage of mass production of the vibration damper to be installed in automotive vehicles, it is important to improve production efficiency of the vibration damper with facility of designing and manufacturing the damper.
It is therefore an object of this invention to provide an improved vibration damping device for an automotive vehicle, which is capable of exhibiting an improved or stabilized damping capability and an improved production efficiency of the vibration damping device, in comparison with the vibration damper disclosed in the above-indicated document of International Publication WO 00/14429.
The above object may be achieved according to the principle of the present invention, which provides a vibration damping device for damping vibrations of a vibrative member of a vehicle, including: (a) a rigid housing member having an accommodation space, which is fixedly disposed in the vibrative member; and (b) an independent mass member having a rigid mass body and an elastic body layer formed on and bonded to an outer surface of the rigid mass body, the outer surface of the rigid mass body having a configuration different from a configuration of an inner surface of the housing member which defines the accommodation space, the independent mass member being non-adhesively disposed in said accommodation space such that an outer surface of the independent mass member is opposed to the inner surface of the housing member with a predetermined gap distance therebetween, to thereby permit displacement of the independent mass member relative to the housing member, the independent mass member and the housing member being brought into elastic impact against each other, upon application of a vibrational load to the device, at respective abutting surfaces thereof which are opposed to each other in a direction in which said vibrational load is applied, the elastic body layer of the independent mass member having a wall thickness which partially varies so that the abutting surface of the independent mass member has a configuration corresponding to that of the abutting surface of the housing member.
In the vibration damping device constructed according to the present invention, the provision of the elastic body layer formed on the outer surface of the rigid mass body makes it possible to adjust the configuration of the abutting surface of the independent mass member so as to correspond to the configuration of the abutting surface of the housing member. This arrangement permits precisely controlling or adjusting the gap distance between the abutting surfaces of the independent mass member and the housing member, even in the case where the outside configuration of the rigid mass body is different from the configuration of the accommodation space, i.e., the configuration of the inner surface of the housing body which defines the accommodation space. Thus, the vibration-damping device of the present invention can effectively exhibit a desired damping effect. It may be possible that the wall thickness of the elastic body layer is arranged so that the entire outside configuration of the independent mass member corresponds to the entire configuration of the accommodation space.
In the vibration-damping device of the present invention, the rigid mass body can be designed and manufactured without the configuration of the housing member taken into account, and vice versa. For instance, the present vibration damping device may employ the rigid mass body having a simple configuration including a cylindrical rod shape and a flat-plate shape, even if the housing member has a complicated configuration so as to meet various kinds of requirements, resulting in an improved degree of freedom in designing or manufacturing the rigid mass body and the housing member.
The rigid mass body may be made of a high gravity material, such as iron, making it possible to effectively obtain the mass body which is made compact in size and which has a sufficiently large mass. While the mass body formed of the rigid material generally suffers from difficulty in processing or machining thereof, the present invention does not require processing the shape of the mass body precisely. Namely, the wall thickness of the elastic body layer formed on the rigid mass body is suitably changed so that the configuration of the abutting surface of the independent mass member corresponds to the configuration of the abutting surface of the housing member. Thus, the present vibration-damping device assures a high dimensional accuracy and improved production efficiency of the independent mass member.
The housing member may be made of metallic materials such as iron or an aluminum alloy, or a synthetic resin material, for example. Preferably, the housing member may be formed of a rigid material having a modulus of elasticity of 5xc3x97103 MPa or more so as to establish a required hardness enough to support the independent mass member and a desired damping effect. The rigid mass body may preferably be formed of metallic materials, such as iron, in view of their high processability. In order to assure an improved damping effect of the present vibration damping device and a reduced impact noise upon impact of the independent mass member with the housing member, the elastic body layer formed on and bonded to the outer surface of the rigid mass body may preferably have a Shore D hardness of 80 or lower, more preferably, within a range of 20-40, as measured in accordance with ASTM method D-2240. For the above-mentioned improved damping effect and the reduced impact noise, the elastic body layer is also arranged to have a modulus of elasticity within a range of 1-104 MPa, more preferably, 1-103 MPa, and a loss tangent is not less than 10xe2x88x923, more preferably within a range of 0.01-10, preferably.
In the present invention, the housing member may be made of a rigid material such as a synthetic material, which has a modulus of elasticity within a range of 5xc3x97103-5xc3x97104 MPa, for example, resulting in a minimized impact noise and an ease of tuning of damping characteristics of the vibration-damping device. In the case where the housing member has a relatively low rigidity, the elastic body layer formed on the housing member may be suitably arranged to have a modulus of elasticity which is made smaller than that of the housing member. More preferably, the modulus of elasticity of the elastic body layer is held within a range of 1-102 MPa. This arrangement makes it possible to assure a desired strength and durability of the housing member, and to improve a damping effect of the vibration-damping device with respect to low frequency vibrations, for example.
For effectively establishing further improved damping effect of the vibration damping device of the present invention, the gap distance between the abutting, surface of the independent mass member and the abutting surface of the housing member, namely, between the outer surface of the elastic body layer and the inner surface of the housing member which defines the accommodation space, is preferably arranged to be held within a range of 0.05-0.8 mm. Accordingly, the independent mass member may be reciprocally movable by a distance of 0.1-1.6 mm between two abutting surfaces of the housing member which are opposed to each other with the independent mass member therebetween, in the direction in which the vibrational load is applied to the vibration-damping device. In order to assure or excite the desired and repeated free displacement or bouncing movement of the independent mass member relative to the housing member, upon application of the vibrational load to the device, the mass of the independent mass member, i.e., the total mass of the rigid mass body and the elastic body layer, may be held within a range of 5-10% of the mass of the vibrative member, whereby the independent mass member moves into and impact the housing member and damps the vibrations excited in the vibrative member.